Lewis Structures, Bond Types, and Molecular Geometry in Chemistry

Lewis model

A bonding theory that emphasizes valence electrons in explaining chemical bonding, using Lewis structures to represent molecules.

Ionic bond

A chemical bond formed by the electrostatic attraction between oppositely charged ions (cation and anion).

Covalent bond

A chemical bond formed when two atoms share one or more pairs of valence electrons.

Metallic bond

A bond formed by the attraction between positively charged metal ions and a sea of delocalized valence electrons.

Valence electrons

The outermost electrons of an atom, involved in chemical bonding.

Lewis structures

Diagrams that show the bonding between atoms in a molecule and the lone pairs of electrons that may exist.

Octet rule

The tendency of atoms to gain, lose, or share electrons so as to have eight electrons in their valence shell.

Bonding pairs

Pairs of electrons shared between atoms in a covalent bond.

Lone pairs (nonbonding pairs)

Pairs of valence electrons that are not shared with another atom.

Single covalent bond

A bond formed when two atoms share one pair of electrons.

Double covalent bond

A bond formed when two atoms share two pairs of electrons.

Triple covalent bond

A bond formed when two atoms share three pairs of electrons.

Polar covalent bond

A covalent bond in which electrons are shared unequally, resulting in partial positive and negative charges.

Electronegativity

A measure of an atom's ability to attract bonding electrons to itself in a chemical bond.

Dipole moment (μ)

A measure of the polarity of a bond or molecule, indicating the separation of positive and negative charge.

Percent ionic character

The percentage of a bond's measured dipole moment compared to what it would be if the bond were completely ionic.

Resonance

The concept that some molecules cannot be represented by a single Lewis structure and instead are a hybrid of two or more contributing structures.

Resonance structures

Two or more Lewis structures for the same molecule that differ only in the placement of electrons.

Formal charge

A calculated charge assigned to an atom in a Lewis structure, assuming electrons in bonds are shared equally.

Free radical

A molecule or ion with an unpaired electron, typically highly reactive.

Expanded octet

A situation where an atom has more than eight electrons in its valence shell, possible for elements in period 3 and beyond.

Bond energy (bond enthalpy)

The energy required to break one mole of a bond in the gas phase.

Bond length

The distance between the nuclei of two bonded atoms.